XIV ORIGIN OF PIGMENTS 259 



fuse pigmentation of the epidermis and cuticle, and 

 there is certainly a marked elimination of pigment 

 in the shell at the moult. The elimination of intro- 

 duced pigment by the skin in the Capitellidae is 

 regarded as evidence that the pigment naturally 

 occurring there is a waste product, but the applica- 

 tion of the same principle to the Crustacea is fraught 

 with obvious difficulties. If conclusions are to be 

 drawn from the fate of introduced pigments, then 

 the pigment of the cuticle in Crustacea is not a waste 

 product ; if, on the other hand, it is the elimination 

 of pigment by a moult which is the criterion, then 

 the pigment is a waste product. 



As a whole, therefore, it would seem that while it is 

 impossible for a physiologist to conceive of pigment 

 being produced in the organism in the haphazard 

 fashion some would have us believe, yet it is at 

 present also impossible to give a universal physio- 

 logical explanation of its origin ; it probably arises in 

 many different ways. As yet the classification of 

 pigments given in the second chapter cannot appar- 

 ently be simplified. 



